Set Kotlin language version to 1.7

Closes gh-28625

Author: poutsma

build.gradle

@@ -277,8 +277,8 @@ configure([rootProject] + javaProjects) { project ->
 
 		compileKotlin {
 			kotlinOptions {
-				languageVersion = "1.6"
-				apiVersion = "1.6"
+				languageVersion = "1.7"
+				apiVersion = "1.7"
 				freeCompilerArgs = ["-Xjsr305=strict", "-Xsuppress-version-warnings", "-opt-in=kotlin.RequiresOptIn"]
 				allWarningsAsErrors = true
 			}